This invention relates to an antenna array system and in particular to an antenna array system used in a cellular communication system.
Antenna arrays for radio communication consisting of a plurality of correlated individual antenna elements are known. Typically, the individual antenna elements are simple dipoles equidistantly situated with a distance of typically half a wavelength. When transmitting the Radio Frequency (RF) signal is fed to all the antenna elements and when receiving the signals from all antenna elements are combined together. Depending on the relative phase difference and amplitude between the signals of each antenna element the combined effect of the entire phase array will have a propagation pattern equivalent to a directional antenna, i.e. more energy will be transmitted or received in some directions than in others.
Antenna array systems for communication systems are known which comprise an antenna array, a beamformer providing a number of fixed beams and a transceiver for each of the fixed beams. In a communication system a signal is received or transmitted using the fixed beam which provides the best communication for that user and switching to another beam will only occur when the signal in the current beam degrades below a threshold.
A problem with the above antenna array systems is that they are complex and result in inflexible resource and hardware allocation to individual beams. Furthermore, traditional antenna arrays comprise technology, which is bulky, expensive and inefficient. Especially, RF (Radio Frequency) power amplification in traditional antenna arrays is associated with high complexity, low efficiency and/or high cost.
The invention seeks to provide a flexible antenna array system with high performance hardware.
According to the present invention, there is provided an antenna array system comprising at least a first antenna array; first beamforming means providing a plurality of beam ports, each beam port being associated with a directional beam of the first antenna array; a plurality of transceiver elements; switching means for associating the plurality of transceiver elements with the plurality of beam ports; wherein the plurality of transceiver elements by the switching means are dynamically associated with the plurality of beam ports in response to a desired beam direction for radio communication supported by each of the plurality of transceiver elements and the association of transceiver elements to beam ports is rearranged at substantially periodic intervals.
This provides for a very efficient and flexible utilisation of resource and transceiver elements.
Preferably, the association of a first transceiver element of the plurality of transceiver elements to beam ports is at least partly in response to a parameter associated with a characteristic of a radio communication supported by a second transceiver element of the plurality of transceiver elements. This allows optimised total performance for all subscriber units served by the antenna array system.
According to a first feature of the invention, the antenna array system has a plurality of beam ports which is larger than the plurality of transceiver elements.
Preferably, the antenna array system further comprises at least a second antenna array providing at least partial diversity with respect to the first antenna array; at least second beamforming means increasing the plurality of beam ports by providing a further plurality of beam ports each being associated with a directional beam of the second antenna array; and wherein the directional beams of the second antenna array are offset and overlapping with respect to the directional beams of the first antenna array.
According to a second feature of the invention, the antenna array system is incorporated in a Time Division Multiple Access communication system, such as GSM, and the switching means are operable to change the association of the plurality of transceiver elements with the plurality of beam ports on a time slot basis.
The transceiver elements can include receiver elements or transmitter elements. Preferably the plurality of transceiver elements comprises transmitter elements and receiver elements and the switching means are operable to independently associate receiver elements and transmitter elements with the plurality of beam ports.